1. Field of the Invention
The present invention relates to a brake control system for a vehicle and particularly, to a brake control system for a vehicle, in which yaw control can be performed by operation of the vehicle brakes.
2. Description of the Related Art
In a prior art brake control system, for example, in Japanese Patent Application Laid-Open No. 2-70561, a wheel brake for an outer wheel during turning of the vehicle, is operated in order to prevent the vehicle from becoming unstable due to external disturbances, such as variations in the friction coefficient of a road surface, a crosswind or a rut in the road.
In the known brake control system, however, when the deviation between a target yaw rate and an actual yaw rate is increased, a yaw control by the brake operation is started, and the brake operation may be started when it is unnecessary. In other words, when a counter steering is applied, yaw control is unnecessary, but the brake operation is started in response to an increase in the deviation between the target yaw rate and the actual yaw rate.
In the above known brake control system, the wheel brake for the outer wheel during turning of the vehicle, is operated in accordance with the deviation between the target and actual yaw rates. However, when the directions of the target and actual yaw rates are the same as each other, it is necessary to apply a large counter moment, whereas when the directions of the target and actual yaw rates are opposite from each other, a relatively small counter moment may be applied as a result of a partial offset of moments due to the opposite turning direction. If the control of the brake operation is conducted merely in accordance with the deviation, the yaw control is not adapted for the operational state of the vehicle.